fail to build rgb2yuv_neon_common.S with clang integrated as

Description

Summary of the bug:
build ffmpeg using clang and it's inegrated as for arm target, for example build for android using clang from ndk without -fno-integrated-as flag. here is details of configure and build error when cross compile for raspberry pi: ​https://travis-ci.org/wang-bin/avbuild/jobs/294735568